1. Field of the Invention
The present invention relates to thin film magnetic heads mounted on, for example, hard disk drives. To be more specific, it relates to thin film magnetic heads composed of a gap layer formed over and/or under a magnetoresistive element layer, which gap layer comprises an improved material or structure so as to have an enhanced thermal conductivity.
2. Description of the Related Art
FIG. 16 is an enlarged sectional view of a conventional thin film magnetic head illustrated from an opposite side of a recording medium.
This thin film magnetic head is a reading head with the use of magnetoresistance effect, and mounted, for instance, on a trailing side edge of a constitutive slider of a floating type head. Onto the thin film magnetic head (reading head) shown in FIG. 16, a so-called inductive head for writing can be laminated.
The reference numeral 1 in FIG. 16 indicates a lower shield layer composed of, for example, sendust or a Ni--Fe alloy (Permalloy; trade mark). Onto the lower shield layer 1 is formed a lower gap layer 20 composed of a non-magnetic material such as Al.sub.2 O.sub.3 (aluminium oxide), and onto the lower gap layer 20, a magnetoresistive element layer 16 is formed.
The magnetoresistive element layer 16 can be classified into an anisotropic magnetoresistive (AMR) element using an element having magnetoresistance effect, and a giant magnetoresistive (GMR) element using an element having giant magnetoresistance effect. For providing higher recording density, a GMR element having a superior regeneration sensitivity is preferably employed. There are some species of structures which produce giant magnetoresistance effect, among which a structure called as a spin-valve type thin film element is comparatively simple and can change its resistance even in a weak magnetic field. The spin-valve type thin film element has the simplest structure composed of four layers, i.e., a free magnetic layer (a Ni--Fe alloy), a non-magnetic electrically conductive layer (Cu), a pinned magnetic layer (a Ni--Fe alloy) and an antiferromagnetic layer (e.g., an Fe--Mn alloy).
As illustrated in FIG. 16, hard bias layer 4 as longitudinal bias layer is formed on both sides of the magnetoresistive element layer 16, and electrode layer 5 composed of a non-magnetic electrically conductive material having a small electric resistance such as Cu (copper) or W (tungsten) is formed on the hard bias layer 4, respectively. When the magnetoresistive element layer 16 is composed of the aforementioned spin-valve type thin film element and a sensing current is applied to the electrode layers 5, the sensing current is to flow in the pinned magnetic layer, non-magnetic electrically conductive layer and free magnetic layer of the spin-valve type thin film element.
Onto the electrode layer 5 an upper gap layer 21 composed of a non-magnetic material such as aluminium oxide is formed, and onto the upper gap layer 21, an upper shield layer 7 composed of sendust or Permalloy is formed, as shown in FIG. 16.
To enhance the regeneration sensitivity of the magnetoresistive element layer 16 for providing a high recording density, the density of a current from the electrode layer 5 should be increased. Increase of the current density, however, invites increase of heat generation from the magnetoresistive element layer 16 and hence elevation of the temperature of element of the magnetoresistive element layer. This is because the gap layers 20 and 21 formed under and over the magnetoresistive element layer 16 are each composed of an insulation film having a low thermal conductivity such as Al.sub.2 O.sub.3.
By way of illustration, when the magnetoresistive element layer 16 is composed of a spin-valve type thin film element, elevation of the temperature of element of the magnetoresistive element layer 16 results in diffusion of nickel in the Ni--Fe alloy constituting the pinned magnetic layer and free magnetic layer, and of copper constituting the non-magnetic layer, which leads to collapse of multilayer structure of the element. The collapse of the multilayer structure in turn decreases a change rate of resistance and hence decreases the regeneration sensitivity. Not only in spin-valve type thin film elements but also in thin film magnetic heads using AMR effect, elevation of the temperature of element invites electromigration so as to impair the durability and to shorten the life time of the elements.